This invention relates to a magnetic recording medium, and more specifically to a magnetic recording medium with desirable running quality and frequency response characteristic.
In general, the magnetic recording medium is made by coating polyester film or other base with a magnetic coating material which consists of powdered .gamma.-Fe.sub.2 O.sub.3 or the like dispersed in a macromolecular resin binder. The nature of the magnetic coating used has important bearings not only upon the running quality and other physical properties but also upon the magnetic characteristic of the medium that is related to the dispersibility of the magnetic particles and other factors, and this nature largely depends on the binding and addition agents chosen. Also, the physical and electromagnetic properties of the medium are closely interrelated. With these in view, a variety of binders for magnetic coating materials have hitherto been introduced, but none have proved fully satisfactory.
The binders thus far employed have been urethanes, vinyl chloride-vinyl acetate copolymers, cellulose plastics, epoxy resins, and polyesters, mostly in combinations of two different resins. The present invention is concerned with improvements in magnetic recording media which use, out of the above-mentioned resins, the vinyl chloride-vinyl acetate copolymers and polyester resins.
The magnetic recording medium whose coating contains a vinyl chloride-vinyl acetate copolymer containing less than 8% vinyl alcohol and a polyester resin as mixed binder gives excellent results in respect of running quality, that is, its ability of being ideally drawn past the magnetic head in a cassette tape deck, particularly in the hot and humid environment (e.g., at 60.degree. C. and 75% RH). It has, however, failed to be quite satisfactory in frequency response characteristic and amelioration in this point has been called for.